gametophyte reduction

Foster and Gifford's text, Comparative Morphology of Vascular Plants,
mentions that there are a few fern species which exist almost entrely as
gametophytes with the sporophytes rare and small (Science 142: 1483-84).
Perhaps they are an illustration of how the sporophyte could possibly
have become reduced and dependent on the gametophyte.
David Hershey
dh321 at excite.com
Dana Ann Dudle wrote:
>> Hi All--
>> After such helpful and interesting responses to my question regarding
> polyploidy, I have decided to try yet another question on y'all:
>> What were the intermediate steps between the dominant, photosynthetic
> gametophyte and reduced sporophyte present in the non-vascular plants
> (bryophytes), and the dominant sporophyte that is present in all vascular
> plants (as far as I have been able to discern). The oldest fossils of
> vascular plants that are most often referenced in textbooks and review
> articles, e.g. Cooksonia and Rhynia, are called sporophytes...
>> IT seems as if this was a very important development in the evolution of
> plants, and yet I have found very little reference as to HOW this change
> occurred. Does anyone know of fossil evidence or living transitional
> forms that may give some insight into this major change in the focus of
> the alternation- of- generations in land plants?
>> I have always been taught that "mosses have dominant gametophytes, and
> ferns have dominant sporophytes", but I have not questioned the "how or
> why" until I started writing lectures and preparing classes on this topic.
>> Any hints or leads would be greatly appreciated (as well as speculations!)
>> Thanks,
> Dana
> *********************************
> Dana A. Dudle
> Dept. of Biological Sciences
> DePauw University
> Greencastle, IN 46135
>ddudle at depauw.edu> *********************************